Manual filling of containers has become generally undesirable in the automated "factory of the future" because of manpower costs and increasingly higher environmental standards for the workplace. The manufacturing environment places exacting demands on the people and tools used to fill containers mounted on a vehicle. When such containers are improperly filled, the fluid will oftentimes appear on the factory floor and/or the vehicle or result in system defects.
Automated fluid fill systems for such containers must easily adapt to production lines of material handling systems. The work cell must be designed to meet the requirements of the vehicle and its components. In addition, control systems must be compatible with factory communication systems. Finally, the systems must be able to compensate for variations in location and attitude due to manufacturing tolerances, cumulative assembly tolerances, vehicle presentation and various vehicle models.
Frequently during a vehicle assembly process, a partially completed vehicle body proceeds down an assembly line while being loosely held by a carrying fixture. The exact position of the body is not known at any work station. It goes without saying that containers for liquids such as fuel, brake fluid, transmission fluid, coolants, windshield wiper fluid, refrigerants, oil, water, etc. mounted on the vehicle also have indeterminate positions. Each container is located within a finite window of uncertainty which is both known and constant.
A related problem is that of non-rigid bodied. In practice it has been observed that "identical" vehicle bodies produced on the same assembly line will often have unpredictable dimensional irregularities. These irregularities and the compliance of a partially completed body have come to be accepted artifacts of modern design and manufacturing practices. It is clear that future manufacturing systems must be able to gracefully tolerate these irregularities.
One possible solution to these problems is to design the entire assembly process to extremely high tolerances to ensure that the vehicle location in space is invariant from one vehicle to the next. Also, it must be ensured that the containers and vehicle bodies are indeed "identical". Such an approach oftentimes requires a relatively high initial investment and expensive retooling costs to fill different containers with different fluids.
Vision systems oftentimes offer immediate advantages in reducing tooling and fixture costs. Vision systems can also provide more accuracy and precision than other methods in determining location. This added accuracy, coupled with precision robots, can be used to accomplish tasks which are presently cost ineffective.
Robots are used in a wide variety of applications in industry such as painting, spot-welding, and sealing. In the mechanical assembly industry, robots are used for palletizing/depalletizing parts and unloading parts from trays for assembly operations. In application areas where the capabilities of the traditional "blind" robot fall short, machine vision becomes an integral part of the robot system to assist in end effector guidance. The totally-integrated, visually-guided robotic system results in enhanced manufacturing productivity, improved quality and reduced fixturing costs, which cannot be achieved with conventional robotic systems.
Applications of machine vision in robotic systems have not all been "success" stories. Many plant engineers still face the formidable task of interfacing vision systems to robots and devote major engineering effort to achieve a workable illumination environment. Though vision systems have often worked well with robots, there is still a broad class of applications which have been marginally operational and which could be better handled with different approaches. There are also many potentially successful vision-robot applications yet to be explored.
Many industrial robotic applications require the accurate positional location of identical components within a finite work area. Typical examples might be the loading or unloading of automotive parts from parts trays, the picking up of a part which has been loosely positioned by a parts feeder, or the identification and location of a part which has been cycled into a work cell for a robotic operation. Experience has shown that the essential problem in many robotic applications is the location of a rigid body which is constrained to movement within a plane. In these two-dimensional cases, the position of the rigid body is completely specified by only three degrees of freedom: The body is only free to slide in the two planar dimensions, and to rotate about an axis perpendicular to the plane.
The U.S. Patents to Blanchard et al 3,618,742, Michaud et al 3,804,270, Birk et al 4,146,924, Pryor et al 4,373,804 and Masaki 4,380,696 disclose machine vision systems which provide visual data which is subsequently processed and put into a form utilized to alter the pre-programmed path of a robot so that the robot can perform work on the object. Such prior art methods and systems, however, are inadequate to solve the compliance and irregularity problems of vehicle bodies and the containers they support in a factory environment.